Head-up displays (HUDs) are known in the art. Such display systems may be used in a variety of different applications such as in military, civil aviation and automotive applications.
A typical HUD includes a data processing unit, an optical projector unit (OPU) (herein below referred to as “projector”), and a see-through display, which is commonly known as a combiner. The projector includes an image source (such as a cathode ray tube (CRT) and a Liquid Crystal Display (LCD)) and optics. The optics includes a set of lenses (e.g., a refractive or diffractive lens) and mirrors, to display the information generated by the image source on the combiner. The combiner allows the user to view the displayed information (e.g., the altitude, airspeed and heading of an aircraft), while maintaining external situational awareness. The displayed information is consisted of computer generated graphics and video images and is herein below referred to as “image”. Thus, the image is combined with the ambient scenery, enabling the user to view both the image and the ambient scene simultaneously. Usually, the projected image appears superimposed onto an image from the ambient scene.
HUD systems may be divided to two types: fixed HUDs, which are fixed to a chassis (such as an airframe of an aircraft, or a chassis of a vehicle), and helmet-mounted or head-mounted HUDs. Fixed HUD systems usually include a combiner, which is rigidly fixed.
Reference is now made to FIGS. 1A and 1B. FIG. 1A is a schematic illustration of a horizontal cross section of an aircraft which includes a fixed Head-up Display system (not shown), as known in the art, while the aircraft is approaching a runway in calm weather. FIG. 1B is a schematic illustration of a horizontal cross section of the aircraft of FIG. 1A, flying against a side wind blowing toward the aircraft, from left of the aircraft.
With reference to FIG. 1A, the fixed Head up Display system includes a combiner 58, which is rigidly fixed to an aircraft 54. A longitudinal axis 60 of aircraft 54 is in line with a heading vector 62 of aircraft 54. During the landing of aircraft 54, a pilot 56 of aircraft 54 flies aircraft 54, such that heading vector 62 is in line with an approach line 64 of a runway 52. As used herein, a horizontal axis of a combiner is defined by a line crossing the combiner, which is substantially parallel to the horizontal plane of the aircraft. A horizontal axis 66 of combiner 58 is perpendicular to longitudinal axis 60 and therefore perpendicular to heading vector 62. Therefore, pilot 56 is able to view the image projected by the fixed Head up Display system on combiner 58, along with the ambient scenery (i.e., runway 52).
With reference to FIG. 1B, due to side wind, indicated by arrows 70, longitudinal axis 60 is tilted relative to heading vector 62. However, pilot 56 still maintains heading vector 62, in line with approach line 64. In this case, horizontal axis 66 of combiner 58 is no longer perpendicular to heading vector 62. Consequently, pilot 56 is unable to view runway 52, through combiner 58. Consequently, the image projected by the system on combiner 58 is at least not properly superimposed on the image of runway 52.
U.S. Pat. No. 3,945,716 issued to Kinder and entitled “Rotatable Head Up Display with Coordinate Reversal Correctives,” is directed to a rotatable head up display system for use as a visual aid for target acquisition and weapon delivery by a pilot from an aircraft. The system includes a head up display arm pivotally mounted to the aircraft, an image projecting means (a CRT unit), which is mounted on the arm, a CRT control unit which contain the CRT unit or controls the CRT unit, and a display plate (or a screen or a holographic lens), which is depending from the arm into a normal field of view of the pilot. The image projecting means projects images onto the display plate. The system further includes a sensor for acquiring and tracking a target, and for transmitting images to the projecting means, while the CRT control unit automatically positions the arm in response to and in coordination with movement of the sensor. The sensor may be moved through automatic sensor control or through a manual controller by a joystick. Thus, the projecting means and the display plate are repositioned and presented substantially along the azimuth of the target.
US Patent Application Publication No. 2005/0206727 to Kormos and entitled “Systems and Method for Forming Images for Display in a Vehicle” is directed to an auxiliary vision system, which forms images for display in land vehicles, and particularly applicable during night time. The system includes a head up display unit, a camera unit, a computer, and one or more sensors, such as an angular encoder. The sensors provide information regarding the heading of the vehicle. The sensors are coupled to a steering column of the vehicle or to an inclinometer which is coupled to a chassis of the vehicle. The sensors may be replaced by image processing software embedded within the computer. The head up display unit includes a liquid crystal display (LCD), a mirror, a drive mechanism and a circuitry. The camera unit includes a lens system, a chopper (which may be omitted in some embodiments), a detector and a circuitry. The detector includes a two-dimensional matrix of detector elements, where each detector element produces a respective pixel of a resulting image. The camera unit is electrically coupled to the head up display unit and to the computer. The computer is electrically coupled to one or more of the sensors. The head up display unit is mounted to the vehicle and projects images onto the inside surface of the windshield for display to a driver. The lens system directs the incoming radiation onto an image plane of the detector. The chopper periodically permits and prevents the travel of incoming infrared radiation to the detector. The circuitry of the camera unit controls the detector, reads out the images it detects, and synchronizes the chopper to the operation of the detector. Furthermore, based on information from the computer, the circuitry sends the information obtained from the detector through the electrical coupling to the circuitry within the display unit. The computer provides instructions to the camera unit based on the heading information it receives from the sensors. Using the heading information, the computer selects the detector elements of the detector for which the associated information should be used, to form an image by the head up display unit. The computer furthermore, sends appropriate instructions regarding these detector elements to the circuitry of the camera unit, which receives the instructions regarding the selected detector elements, and sends the information associated with each selected detector element to the head up display unit. The circuitry of the display unit takes successive images obtained from the detector through the circuitry of the camera unit, and presents them on the LCD. The LCD image is projected onto the mirror that reflects the image which is directed onto the inner surface of the windshield, thus creating a virtual image for the driver. The mirror is movably supported, and its position in any given time is supported by the drive mechanism. Using the drive mechanism, the driver may adjust the mirror so that the image on the windshield is in a viewing position comfortable for the driver. Once the driver has finished adjusting the mirror to a suitable position, it remains in that position during normal operation of an auxiliary vision system.